Near-optimal two-mode spin squeezing via feedback

We propose a feedback scheme for the production of two-mode spin squeezing. We determine a general expression for the optimal feedback, which is also applicable to the case of single-mode spin squeezing. The two-mode spin squeezed states obtained via this feedback are optimal for j=1/2 and are very close to optimal for j>1/2. In addition, the master equation suggests a Hamiltonian that would produce two-mode spin squeezing without feedback, and is analogous to the two-axis countertwisting Hamiltonian in the single mode case.Comment: 10 pages, 6 figures, journal versio

Spin squeezing via quantum feedback

We propose a quantum feedback scheme for producing deterministically reproducible spin squeezing. The results of a continuous nondemolition atom number measurement are fed back to control the quantum state of the sample. For large samples and strong cavity coupling, the squeezing parameter minimum scales inversely with atom number, approaching the Heisenberg limit. Furthermore, ceasing the measurement and feedback when this minimum has been reached will leave the sample in the maximally squeezed spin state.Comment: 4 pages, 3 figures, revtex

Laser-based metastable krypton generation

We demonstrate the generation of metastable krypton in the long-lived 1s^{5} state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p^{6} state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.M. A. Dakka, G. Tsiminis, R. D. Glover, C. Perrella, J. Moffatt, N. A. Spooner, R. T. Sang, P. S. Light, and A. N. Luite

Geographical and temporal distribution of SARS-CoV-2 clades in the WHO European Region, January to June 2020

We show the distribution of SARS-CoV-2 genetic clades over time and between countries and outline potential genomic surveillance objectives. We applied three available genomic nomenclature systems for SARS-CoV-2 to all sequence data from the WHO European Region available during the COVID-19 pandemic until 10 July 2020. We highlight the importance of real-time sequencing and data dissemination in a pandemic situation. We provide a comparison of the nomenclatures and lay a foundation for future European genomic surveillance of SARS-CoV-2.Peer reviewe

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362

Population dynamics in a metastable neon magneto-optical trap

We observe the population dynamics within a metastable neon magneto-optical trap (MOT) through the measurement of the average squared Clebsch-Gordan coefficient C 2 over a range of laser detunings. The magnitude of C 2 is dependent on the internal quantum state of an atom interacting with the light field and is found to show a strong dependence on the applied laser detuning. Previously it has been reported [Townsend et al., Phys. Rev. A 52, 1423 (1995)] that trapped atoms in a MOT are pumped towards the states that interact most strongly with the local field and therefore the measured value of C 2 is larger than the average over all possible transitions. For the 3 P 2 -to- 3 D 3 cooling transition in metastable neon the average C 2 value is equal to 0.46; however, we have measured 0.29 ± 0.03 < C 2 < 0.73 ± 0.09 . We explain this range of values for C 2 by considering the possible transition rates between the different magnetic sublevels in the system. This result has significant consequences when trap populations are measured via fluorescence in a MOT.R. D. Glover, J. E. Calvert and R. T. San

Strong-field ionization of argon: Electron momentum spectra and nondipole effects

©2022 American Physical SocietyWe investigate the influence of relativistic nondipole effects on the photoelectron spectra of argon, particularly in the low-kinetic-energy region (0-1 eV). In our experiment, we use intense, linearly polarized 800-nm laser pulses to ionize Ar from a jet and we record photoelectron energy and momentum distributions using a reaction microscope. Our measurements show that nondipole effects can cause an energy-dependent asymmetry along the laser propagation direction in the photoelectron energy and momentum spectra. Model simulation based on the time-dependent Dirac equation can reproduce our measurement results. Moreover, the electron trajectory analysis based on the classical model reveals that the photoelectrons obtain a negative momentum shift in the laser propagation direction due to the interplay between the Lorentz-force-induced radiation pressure during its free propagation in the continuum and rescattering by the Coulomb potential of the parent ion when it is driven back by the laser field.11Nsciescopu

Frustrated tunnel ionization in the few-cycle regime

Frustrated tunnel ionization (FTI) is one of the dominant channels in strong field ionization that results in the excitation of atoms. Recent studies have shown that there is a significant number of FTI events for multi-cycle pulses with the theory predicting that the excitation efficiency increases with pulse duration decreasing into the few-cycle regime. Our work concentrates on experimentally investigating the effect of few-cycle pulses on the FTI excitation process. We use pulses with duration 6 fs centred at 800 nm at intensities up to 0.8 PW crossed with an atomic Ar beam. We find that with few-cycle pulses there is more FTI per tunneling event and that for the same pulse energy more FTI is generated.R. D. Glover, D. Chetty, B. A. deHarak, A. J. Palmer, M. A. Dakka, J. L. Holdsworth, I. V. Litvinyuk, A. N. Luiten, P. S. Light, R. T. San